are hcg blood tests 100% accurate??

[dmestiza]

my last menstrual period was from jan 8th-jan 15th & i have had no periods until now... and i had sex with my husband on jan 17th & on the 21st... i had a hcg blood test on march 2nd and it was negative... but im wondering if hcg blood tests are 100% accurate/correct... or if some women can detect to be positive/pregnant on a blood test abit later on in pregnancy?!?!? any help will do! thank you all!

 

[x-ginge-x]

At the time they are taken yes they are almost 100% accurate, I think you are not pregnant and that you are having issues with your monthly cycle. A doctor will be able to investigate this further.